1. Field of the Invention
The invention relates to an image sensor device with a shifted microlens array and more particularly to a microlens shift calculation for the microlens array.
2. Description of the Related Art
As optoelectronic applications, such as digital cameras, digital video recorders, image capture capable mobile phones and monitors, become more and more popular, the demand for image sensor devices accordingly increase. An image sensor device is used for recording a change of a photo signal from an image and converting the photo signal into an electronic signal. After recording and processing the electronic signal, a digital image is generated. In general, image sensor devices can be categorized into two main types, one is charge coupled devices (CCD) and the other complementary metal oxide semiconductor (CMOS) devices.
The image sensor device typically comprises a pixel array. Each pixel includes a photosensor that produces a signal corresponding to the intensity of light impinging on the photosensor. When an image is focused on the array, signals can be employed to display a corresponding image. In conventional technology, a microlens array is correspondingly disposed above the pixel array and used for focusing light onto the pixel array. However, despite the use of the microlens array, a large amount of incident light is not directed efficiently onto the photosensors due to the geometry of the pixel array. Different pixels of the pixel array may receive light with different chief ray angles (CRA), depending on the pixel location in the pixel array. For example, a central pixel of the pixel array may receive light with a chief ray angle of 0 degrees and peripheral pixels of the pixel array may receive light with chief ray angles up to about 25 to 30 degrees. Thus, both the intensity and the focal depth of the incident light to each pixel/photosensor are varied as the chief ray angle varies. The varied light intensities and focal depths may enhance shading effect and cross-talk of pixels, resulting in reduction of the signal to noise ratio (SNR) and photosensitivity of the image sensor device.
Therefore, there is a need to develop a novel design for a microlens array capable of enhancing coupling efficiency of pixels and reducing cross-talk of pixels.